Intracellular Ca2+ plays a pivotal role in various cell functions, ranging from exocytosis and contraction to gene expression and cell differentiation, proliferation and apoptosis. Human mutations in the genes involved in intracellular Ca2+ handling result in visual defects, diabetes mellitus, disorders in the skin, skeletal-muscle, nervous, cardiac and vascular systems (reviewed by Missiaen et al., 2000). In addition to the well characterized voltage-dependent Ca2+ channels, Ca2+ pumps and Ca2+-permeable ligand-gated channels, TRPC (Transient Receptor Potential Channels) is an emerging class of Ca2+-permeable cation channel superfamily. All of the channels in this family contain a six-trans-membrane domain although various cellular mechanisms have been implicated in their functions (reviewed by Harteneck et al., 2000).
The first member of this family, dTRP, was identified from Drosophila mutants trp whose photoreceptors failed to generate a sustained receptor potential in response to intense sustained light. The mutant fly showed a reduced Ca2+ selectivity of the light response and the channel activity of dTRP depended on PLC activation was also demonstrated. Later, many mammalian homologues have been cloned and based on their homology, they are divided into three subfamilies: short (s), osm (o) and long (1). The sTRPC subfamily includes TRP1–7. Although the specific physiological function of each isoform remains to be assigned, it is generally believed that they may be involved in Ca2+ entry after activation of receptors coupling to PLC. The TRP2 is specifically expressed in vomeronasal organ and involved in pheromone sensory signaling (Liman, et al., 1999). TRP1 and TRP6 are functioned in vascular smooth muscle cells and may play a role in controlling smooth muscle tone, arteriosclerosis and neointimal hypoerplasia (Inoue et al., 2001; Xu & Beech, 2001). It has been shown that TRP4−/− mice lack an endothelial store-operated Ca2+ current, which leads to reduced agonist-dependent vasorelaxation (Freichel et al., 2001).
The first member of oTRPC Subfamily is OSM-9 cloned from C. elegans. It is involved in responses to odorants, high osmotic strength, and mechanical stimulation. Recently, several mammalian homologues including vanilloid receptor (VR1) and vanilloid receptor-like receptor (VRL-1), which may have functions in pain and heat perception (Caterina, 1999; Caterina et al., 2000). VR1 has also been shown to be the receptor of anandamide and mediating its vasodilation effect (Zygmunt et al., 1999). OTRPC4 is an osmotically activated channel and a candidate osmoreceptor, may be involved in regulation of cellular volume (Strotmann et al., 2000). CaT1 & ECaC1 may be the calcium-release-activated calcium channel and involved in Ca2+ reabsorption in intestine and kidney (Peng, et al, 1999; Yu et al., 2001).
The function of the lTRPC is less clear. The cloned mammalian lTRPC includes melastatin 1/MLSN1/LTRPC1, MTR1/LTRPC5, TRPC7/LTRPC2 and TRP-P8. It is known that melastatin 1 is down regulated in metastatic melanomas (Duncan et al., 1998) and MTR1 is associated with Beckwith-Wiedemann syndrome and a predisposition to neoplasias (Prawitt et al., 2000). TRPC7 is mapped to the chromosome region linked to bipolar affective disorder, nonsyndromic hereditary deafness, Knobloch syndrome and holosencephaly (Nagamine et al., 1998). TRP-P8 is a prostate-specific gene and up-regulated in prostate cancer and other malignancies (Tsavaler et al., 2001). A recently cloned TRP-PLIK/hSOC-2/hCRAC-1 exhibits a very interesting feature in that it is a bi-functional protein with kinase and ion channel activities (Runnels et al., 2001). Additionally, a very long TRPC homologue NOMPC was found in Drosophila and C. elegans. NOMPC was identified as a mechanosensitive channel that can detect sound, pressure or movement changes (Walker et al., 2000).
Characterization of the TRP-PLIK2 polypeptide of the present invention led to the determination that it is involved in the modulation of the NFkB pathway, either directly or indirectly.
The fate of a cell in multicellular organisms often requires choosing between life and death. This process of cell suicide, known as programmed cell death or apoptosis, occurs during a number of events in an organisms life cycle, such as for example, in development of an embryo, during the course of an immunological response, or in the demise of cancerous cells after drug treatment, among others. The final outcome of cell survival versus apoptosis is dependent on the balance of two counteracting events, the onset and speed of caspase cascade activation (essentially a protease chain reaction), and the delivery of antiapoptotic factors which block the caspase activity (Aggarwal B. B. Biochem. Pharmacol. 60, 1033–1039, (2000); Thomberry, N. A. and Lazebnik, Y. Science 281, 1312–1316, (1998)).
The production of antiapoptotic proteins is controlled by the transcriptional factor complex NF-kB. For example, exposure of cells to the protein tumor necrosis factor (TNF) can signal both cell death and survival, an event playing a major role in the regulation of immunological and inflammatory responses (Ghosh, S., May, M. J., Kopp, E. B. Annu. Rev. Immunol. 16, 225–260, (1998); Silverman, N. and Maniatis, T., Genes & Dev. 15, 2321–2342, (2001); Baud, V. and Karin, M., Trends Cell Biol. 11, 372–377, (2001)). The anti-apoptotic activity of NF-kB is also crucial to oncogenesis and to chemo- and radio-resistance in cancer (Baldwin, A. S., J. Clin. Inves. 107,241–246, (2001)).
Nuclear Factor-kB (NF-kB), is composed of dimeric complexes of p50 (NF-kB1) or p52 (NF-kB2) usually associated with members of the Rel family (p65, c-Rel, Rel B) which have potent transactivation domains. Different combinations of NF-kB/Rel proteins bind distinct kB sites to regulate the transcription of different genes. Early work involving NF-kB suggested its expression was limited to specific cell types, particularly in stimulating the transcription of genes encoding kappa immunoglobulins in B lymphocytes. However, it has been discovered that NF-kB is, in fact, present and inducible in many, if not all, cell types and that it acts as an intracellular messenger capable of playing a broad role in gene regulation as a mediator of inducible signal transduction. Specifically, it has been demonstrated that NF-kB plays a central role in regulation of intercellular signals in many cell types. For example, NF-kB has been shown to positively regulate the human beta-interferon (beta-IFN) gene in many, if not all, cell types. Moreover, NF-kB has also been shown to serve the important function of acting as an intracellular transducer of external influences.
The transcription factor NF-kB is sequestered in an inactive form in the cytoplasm as a complex with its inhibitor, IkB, the most prominent member of this class being IkBa. A number of factors are known to serve the role of stimulators of NF-kB activity, such as, for example, TNF. After TNF exposure, the inhibitor is phosphorylated and proteolytically removed, releasing NF-kB into the nucleus and allowing its transcriptional activity. Numerous genes are upregulated by this transcription factor, among them IkBa. The newly synthezised IkBa protein inhibits NF-kB, effectively shutting down further transcriptional activation of its downstream effectors. However, as mentioned above, the IkBa protein may only inhibit NF-kB in the absence of IkBa stimuli, such as TNF stimulation, for example. Other agents that are known to stimulate NF-kB release, and thus NF-kB activity, are bacterial lipopolysaccharide, extracellular polypeptides, chemical agents, such as phorbol esters, which stimulate intracellular phosphokinases, inflammatory cytokines, IL-1, oxidative and fluid mechanical stresses, and Ionizing Radiation (Basu, S., Rosenzweig, K, R., Youmell, M., Price, B, D, Biochem, Biophys, Res, Commun., 247(1):79–83, (1998)). Therefore, as a general rule, the stronger the insulting stimulus, the stronger the resulting NF-kB activation, and the higher the level of IkBa transcription. As a consequence, measuring the level of IkBa RNA can be used as a marker for antiapoptotic events, and indirectly, for the onset and strength of pro-apoptotic events.
Using the above examples, it is clear the availability of a novel cloned transient receptor potential channel family provides an opportunity for adjunct or replacement therapy, and are useful for the identification of transient receptor potential channel agonists, or stimulators (which might stimulate and/or bias transient receptor potential channel function), as well as, in the identification of transient receptor potential channel inhibitors. All of which might be therapeutically useful under different circumstances.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of TRP-PLIK2, TRP-PLIK2b, TRP-PLIK2c, and TRP-PLIK2d polypeptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the TRP-PLIK2, TRP-PLIK2b, TRP-PLIK2c, and TRP-PLIK2d polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.